The difference: a 32nm, 69mm² Apple A5 chip. The original had a 45nm, 122mm² A5.

So far as can be told, Apple was still shipping 45nm versions when it cut the 16GB iPad 2 price to £329, from £399, when it launched the iPad 3.

The new version has begun slipping into the supply chain, website AnandTech discovered. The site's benchmarking suggests the new model delivers between 15.8 per cent - for surfing - and 29.1 per cent - when gaming - better battery life.

The snag: there's no way of seeing whether an iPad 2 is a 2,1 or a 2,4 without opening the box and running software capable of extracting that data from the device.

The white 2,4 appears to be shipping as Apple Part Number MC979LL/A. According to Apple's online store, the white 16GB iPad 2 it is selling is the MC989LL/A. Over here, it's the MC954LL/A. Black units have entirely different model numbers too. But eyeing up part numbers doesn't appear to be a successful way of ID-ing the 32nm machines.

But presumably, as Apple sells out of 2,1 stock, it will be replaced by 2,4 units. ®